Physics · Science General

Optics and Light Properties

2,019 Questions

Optics and light properties focus on the behavior of light, including reflection, refraction, dispersion, and polarization. This topic also covers the wave nature of light, illumination, and the functioning of optical instruments like microscopes. Questions on these concepts are common in general science sections of SSC, Railways, and State exams.

Reflection and mirrorsRefraction and mediumsLight wave theoriesPolarization and intensity

Optics and Light Properties Questions

Multiple choice problems on prism prism ray optics and optical instruments optics physics

A ray of monochromatic light is incident on the refracting face of a prism (angle $75^o$). It passes through the prism and is incident on the other face at the critical angle. If the refractive index of the prism is $\sqrt 2$, then the angle of incidence on the first face of the prism is :

  1. $15^o$
  2. $30^o$
  3. $45^o$
  4. $60^o$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
As the ray on the other face is incident on critical angle $r^{'}=sin^{-1}\dfrac{1}{\mu}=sin^{-1}\dfrac{1}{\sqrt{2}}=45^o$

So the refracting angle on first surface $r=A-r^{'}=75^o-45^o=30^o$

Applying snell's law for first surface,

$\mu _{1}sin\alpha _{1}=\mu _{2}sin\alpha _{2}$ 

$1\times sin i=\sqrt{2}sin30^o$

$i=45^o$, hence option $C$ is correct. 
Multiple choice problems on prism prism ray optics and optical instruments optics physics

A beam of light consisting of red, green, and blue colors is incident on a right-angled prism. The refractive indices of the material of the prism for the above red, green, and blue wavelengths are 1.39, 1.44, and 1.47, respectively. The prism will

  1. separate part of the red color from the green and blue color

  2. separate part of the blue color from the red and green color

  3. separate all the three colors from one another

  4. not separate even partially any color from the other two colors
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The prism will separate part of the red color from the green and blue color as the refractive index are different hence they undergo different deviations
hence correct option is $A$.

Multiple choice problems on prism prism ray optics and optical instruments optics physics

A thin prism of angle $7^o$ made of glass of refractive index $1.5$ is combined with another prism made of glass of $\mu =1.75$ to produce dispersion without deviation. The angle of second prism is :

  1. $7^o$
  2. $4.67^o$
  3. $9^o$
  4. $5^o$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The condition for dispersion without deviation is (mu1 - 1) * A1 + (mu2 - 1) * A2 = 0. Using the given values, we solve for A2.

Multiple choice problems on prism prism ray optics and optical instruments optics physics

A spectrum is obtained by sending a beam of white light through a prism. A second prism exactly similar to the first one is placed in an inverted position with the sides parallel to the first. Now

  1. A new spectrum will be formed on the screen with double the number of colours present in the previous spectrum

  2. New spectrum will be obtained on the screen with only half the number of colours present in the previous spectrum

  3. Previous spectrum will disappear and we will obtain a white light formed by the fusion of the colours

  4. A spectrum with same number of colours present in the previous spectrum will be formed but their wave lengths will be increased twice
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A spectrum is obtained by sending a beam of white light through a prism. A second prism exactly similar to the first one is placed in an inverted position with the sides parallel to the first. Now the previous spectrum will disappear and we will obtain a white light formed by the fusion of the colours.

As white is composed of seven colors. The seven colors together joins to form white light again. 

Multiple choice problems on prism prism ray optics and optical instruments optics physics

A number of thin prism of prism angle $A$ and refractive index $\mu$ are arranged on periphery of circle such that any light ray entering from one prism move along a regular polygon

  1. number of prism used will be $\cfrac { 4\pi }{ (\mu -1)A } $
  2. If $A$ is rational, $\mu$ must be rational
  3. if $A$ is rational, $\mu$ must be irrational
  4. If $A$ is irrational, $\mu$ must be irrational
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Deviation by one prism: $\delta = (\mu-1)A$


$\therefore$ Deviation of $n$ prism: $\delta' = n\delta = n(\mu-1)A$       

Deviation of light moving along a regular polygon, $\delta' = 2\pi$

$\therefore$   $n(\mu-1)A = 2\pi$          

$\implies n = \dfrac{2\pi}{(\mu -1)A}$

Thus if $A$ is rational, then $\mu$ must be irrational.

Multiple choice problems on prism prism ray optics and optical instruments optics physics

A ray of light is incident on the hypotenuse of a right-angled prism after travelling parallel to the base inside the prism. If $\mu $ is the refractive index of the material of the prism, the maximum value of the base angle for which light is totally reflected from the hypotenuse is :

  1. $sin^{-1}\left ( \dfrac{1}{\mu } \right )$
  2. $tan^{-1}\left ( \dfrac{1}{\mu } \right )$
  3. $sin^{-1}\left ( \dfrac{\mu -1}{\mu } \right )$
  4. $cos^{-1}\left ( \dfrac{1}{\mu } \right )$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
If  $\alpha$  is maximum value of base angle for which light is totally reflected from the hypotenuse and  $\theta$  is the minimum value of angle of incidence at hypotenuse for total internal reflection.
Then ,
$ \theta =sin^{-1}\left (  \dfrac{1}{\mu}\right )$

$\alpha +\theta =90^o$

$\Rightarrow \alpha = 90^o-sin^{-1}\left ( 1/\mu \right )=cos^{-1}\left ( 1/\mu \right )$
Multiple choice problems on prism prism ray optics and optical instruments optics physics

A thin prism of angle $15^{o}$ made of glass of refractive index $\mu _{1} = 1.5$ is combined with another prism of glass of refractive index $\mu _{2} = 1.75$. The combination of the prism produced dispersion without deviation. The angle of the second prism should be :

  1. $5^{o}$
  2. $7^{o}$
  3. $10^{o}$
  4. $12^{o}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For without deviation 

$\frac{A}{A'}=-\frac{\mu ' -1}{\mu -1}$

$\frac{15^{o}}{A'}=-\frac{1.75-1}{1.50-1}$

$\frac{15^{o}}{A'}=-\frac{0.75}{0.50}$

$A'=-10^{o}$

Multiple choice problems on prism prism ray optics and optical instruments optics physics

A glass prism has a right-triangular cross-section ABC, with $\angle$A$=90^o$. A ray of light parallel to the hypotenuse BC and incident on the side AB emerges grazing the side AC. Another ray, again parallel to the hypotenuse BC, incident on the side AC suffers total internal reflection at the side AB. Find the range of  the refractive index $\mu$ of the material of the prism?

  1. $\sqrt{\dfrac{3}{2}} < \mu < \sqrt 2$
  2. $\mu > \sqrt 3$
  3. $\mu < \sqrt{\dfrac{3}{2}}$
  4. $\sqrt 2 < \mu < \sqrt 3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The conditions provided for grazing emergence and total internal reflection define the boundaries for the refractive index mu based on the geometry of the right-angled prism.

Multiple choice problems on prism prism ray optics and optical instruments optics physics

A thin prism $P _1$ with angle $6^o$ and made from glass of refractive index 1.54 is combined with another thin prism $P _2$ of refractive index 1.72 to produce dispersion without deviation. The angle of prism $P _2$ will be.

  1. $4^o 30'$
  2. $8.5^o$
  3. $6.5^o$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

We know that for small angle of prism, deviation ,$\delta=A(\mu-1)$

where $A$=angle of prism

Here, net deviaton$A _1(\mu _1-1)-A _2(\mu _2-1)=0$

$\implies A _2=\dfrac{A _1(\mu _1-1)}{\mu _2-1}$

$\implies A _2=\dfrac{6\times 0.54}{0.72}=4.5^{o}$

$\implies A _2=4^{o}30'$

Answer-(A)

Multiple choice problems on prism prism ray optics and optical instruments optics physics

The refracting angle of a prism $60^{\mathrm{o}}$.The refractive index of the material of the prism is $\sqrt{\dfrac{7}{3}}$. The limiting angle of incidence of a ray that will be transmitted through the prism in this case will be :

  1. $30^{0}$
  2. $45^{\mathrm{o}}$
  3. $40^{\mathrm{o}}$
  4. $50^{\mathrm{o}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The limiting angle of incidence is determined by the condition that the ray must be able to pass through the prism without undergoing total internal reflection at the second face.

Multiple choice physics air, winds and cyclones the concept of bernoulli's principle air exerts pressure wind and pressure wind and rain uneven heating of earth

The continuous spectrum is obtained when the incandescent substance is?

  1. In state of atomic vapour

  2. In solid state

  3. In state of molecular vapour

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

An incandescent light bulb produces a continuous spectrum because the source of the light is a metal filament (i.e. solid).

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

You see lightning before you hear the thunder because

  1. Lightning is much brighter than thunder.

  2. Thunder is heavier than lightning.

  3. Light can travel through air but sound cannot.

  4. Sound travels slower than light.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Answer is D.

Lightning and thunder are produced simultaneously, but the thunder is heard a few seconds after the lightning is seen. This is because the speed of light in air is more than the speed of sound in air.The speed of light is given as $3\times { 10 }^{ 8 }m/s$. The speed of sound is 340 m/s.
Hence, the flash of lightning is seen before the thunder is heard as the speed of sound is less than speed of light.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

An observer measures speed of light to be C when he is stationary with respect to the source. If the observer moves with velocity $\displaystyle v$ towards the source then the velocity of light observed will be :

  1. $\displaystyle c- v$
  2. $\displaystyle c + v$
  3. $\displaystyle \sqrt{1-v^2/c^2}$
  4. $\displaystyle c$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Speed of light does not change with the frame of reference.  Option 'D' is correct.

Multiple choice physics reflection of light and shadow beam of light ray and beam ray optics

Which of the following is correct for the beam which enters the medium ? 

  1. Travel as a cylindrical beam

  2. Diverge

  3. Converge

  4. Diverge near the axis and converge near the periphery
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since the refractive index is less at beam boundary, the ray at the edges of the beam move faster compared to the axis of beam. Hence the beam converges.

Multiple choice physics reflection of light and shadow beam of light ray and beam ray optics

If a parallel beam of light having intensity I is incident normally on a perfectly reflecting surface, the force exerted on the surface, equal F. When the surface is held at an angle $ \theta $ the force is 

  1. $ 2F tan \theta $
  2. $ F cos \theta $
  3. $ F cos^2 \theta $
  4. $ 2 F $
Reveal answer Fill a bubble to check yourself
A Correct answer